1. Field of the Invention
The present invention relates to an image-forming device such as a laser printer, and a belt unit installed therein.
2. Description of Related Art
In a color laser printer of a tandem type, process cartridges corresponding to the colors of yellow, magenta, cyan, and black are disposed in parallel in the horizontal direction.
In the color laser printer of the tandem type, an endless belt is supported in a circumferentially movable manner on a plurality of rollers, and is disposed in contact from below with photosensitive drums for each color. Paper is conveyed by the belt so as to pass between the belt and each photosensitive drum in sequence, and a toner image that is supported on each photosensitive drum is transferred in an overlapping manner onto the paper during the conveying. This ensures that a multicolor image is formed on the paper at substantially the same speed as that of forming a monochromatic image.
Japanese Patent No. 3439732 has proposed an image forming device with a belt unit. An endless belt is provided in the belt unit, and is in contact with photosensitive drums from below when the belt unit is mounted in the image forming device. The Japanese Patent has proposed a mechanism of removing the belt unit from the image forming device by first moving the belt unit downward to separate the endless belt from photosensitive drums, and then by moving the belt unit in the horizontal direction parallel to the direction in which the endless belt conveys paper on its upper surface.